NATO is only obliged to collectively defend its own member states against attack from outside. Many European politicians must currently be secretly relieved by the existence of the principle. If Ukraine were a member of NATO, the annexation of Crimea in March would have plunged the Western alliance into an immediate military confrontation with Russia.

Yet only a few years ago, there was serious discussion about inviting Ukraine and Georgia to join the alliance. At the 2008 NATO summit in Bucharest, the United States, under President George W. Bush, campaigned vehemently in favor. However, several European states - including Germany - had misgivings, because even then they were concerned about the possibility of serious tensions with Russia.

Today, Berlin is more convinced of this than ever. Michael Gahler is the spokesperson on security policy issues for the conservative European People's Party (EPP) group in the European parliament. He points out that in 2008, there also wasn't a clear majority of Ukrainians in favor of the idea. Gahler said that adopting restraint with regard to Russia was tied to the expectation "that Russia would respect this, and behave accordingly."

Georgia as forerunner

The Americans, however, are still aggressively in favor of accession. Last weekend, on a visit to the Georgian capital, Tbilisi, US Defense Secretary Chuck Hagel said that his country would continue to push for Georgia to join NATO. The US is also considering selling military helicopters to the country.

There are clear parallels between Georgia and Ukraine. Many people see the Russian occupation of the Georgian territories of Abkhazia and South Ossetia in 2008 as the forerunner for the annexation of Crimea in 2014. There was a storm of protest back then, too, but the West did not intervene and appeared to come to terms with the new situation.

In the United States, both Democrat politician Robert Menendez, chairman of the US Senate Foreign Relations Committee, and the Republican Senator John McCain have spoken out in favor of supplying weapons to the Ukrainian army. But Western European politicians believe Russian President Vladimir Putin would see this as a provocation, and tantamount to handing him an excuse to invade.

Will Ukraine become a second Afghanistan?

There are therefore two very different, conflicting interpretations of the situation. The majority of European NATO states do not want to unnecessarily provoke Russia, while the US and some of NATO's eastern members who suffered under Soviet occupation argue the opposite. They point out that if Ukraine were already a NATO member, it might have deterred Putin from his Crimean adventure.

Roland Freudenstein, a security policy expert with the Brussels think-tank Wilfried Martens Center, believes that the refusal to make concrete plans for membership in 2008 "strongly encouraged Putin to embroil Georgia in a war." Stronger military ties to NATO would at least have made Russian aggression less likely, he told DW.

Freudenstein is now in favor of providing limited military support to the Ukrainian forces, "in order to repulse completely unprovoked aggression, or at least to drive the cost of it up so high that the Kremlin will reconsider such action." Russia, he said, does not have "unlimited possibilities for intervention," and the "disaster in Afghanistan" will still be fresh in its memory.

The EPP's Michael Gahler stressed that "not even Russia would claim that Ukraine intends to threaten Russian territorial integrity." Ukraine's military actions are, he said, purely defensive.

No sphere of influence for Russia

Both Freudenstein and Gahler reject the idea of granting Russia a "sphere of influence," which many Western politicians have implied could be a possibility.

The two experts said that every country has the right to choose its alliances freely, and that NATO membership for the two countries must also remain a possibility, at least in principle. Freudenstein added that excluding Ukraine and Georgia "would constitute a reward for Russia's conduct."

However, Gahler said that "stable majority support from the population" would be a requirement, as would the approval of any such accession by all current NATO member states. The latter is certainly not in the cards at present. Whether that changes, said Gahler, also depends on "what kind of a Russia we will be dealing with in future." With Putin's Russia it would not be feasible, he added.

But both experts agree that this doesn't mean the West should simply stand by and do nothing. "NATO and the EU need a new Ostpolitik," said Freudenstein. The EU should, he said, make approaches to civil society and consolidate relationships with elites by way of trade, grants and the lifting of visa restrictions. NATO should also, he said, continue military cooperation beneath the membership threshold, "whether or not that pleases the men in the Kremlin."

Gahler also backed greater civil and military cooperation, but added that at the same time it's important "to continue the dialogue between the EU and Russia," and to closely follow the dialogues between Russia and Ukraine, Georgia and Moldova. There are many differences between America and Europe where dealings with Russia are concerned, as well as among the Europeans themselves, but presumably these are demands on which all are able to agree.